This invention relates to an oil type damper for damping opening and closing motions of lids and drawers in various devices. More particularly, this invention relates to improvements in and concerning oil dampers of simple construction for effectively damping and moderating opening and closing motions of lids or the like by utilizing the resistance offered by the viscosity of an oil such as silicone grease.
In cassette tape recorders and video tape recorders, for example, are used dampers which are adapted to damp and moderate the opening and closing motions of audio and video tape holders. These dampers protect the recorders from vibrations and impacts that would otherwise be caused by the forceful opening and closing motions of their tape holders and thus help to keep the recorders in good operating condition. The dampers having this function broadly fall into two types; the friction type (disclosed in Japanese Utility Model Application Disclosure No. Sho 55(1980)-75805, for example) and the oil type using viscous oil (disclosed in U.S. Pat. No. 4,342,135 and Japanese Utility Model Application Disclosure No. Sho 57(1982)-8604, for example).
The dampers of the former friction type cannot be expected to provide smooth opening and closing motions. Worse still, they suffer gradual degradation of their performance by aging.
Now, the basic construction of a conventional damper of the latter type will be described with reference to FIGS. 1 and 2. This conventional damper comprises two parts of a rotor a and a base seat b. The rotor a is composed of a toothed wheel 1 for receiving a rotational input from an external source, a boss 2 formed integrally and concentrically with the toothed wheel 1, a hollow part 3 formed continuously in the toothed wheel 1 and the boss 2. The base seat b comprises a base 4 adapted to be attached to a given device, a tubular part 5 fastened to the base 4 and adapted to be fitted around the boss 2, and a shaft 6 formed concentrically with the tubular part 5, fastened similarly to the base 4 and adapted to be inserted into the hollow part 3. The oil type damper which is assembled by applying oil such as silicone grease to the inner and outer peripheral surfaces of the boss 2 and/or to the inner peripheral surface of the tubular part 5 and the outer surface of the shaft 6, inserting the shaft 6 into the hollow part 3 of the boss 2 and, at the same time, fitting the boss 2 to the inner surface of the tubular part 5 has been known to the art. This damper is designed to operate by having the rotor a fitted to the base seat b and is not provided with any means capable of preventing leakage of silicone grease from the frictional surfaces. During the summer, for example, the oil is thermally expanded and forced out of the interior of the damper and, as a result, the damper fails to provide its prescribed effect of damping and moderating the rotational motions in the device in which the damper is used. To preclude this trouble, there may be conceived the idea of sealing the interface between the tubular part 5 and the boss 2 with an O-ring thereby preventing otherwise possible leakage of the oil. In this case, the O-ring must be forcibly set in position in the interface between the tubular part 5 and the boss 2. The friction consequently generated between these two parts surpasses the resistance offered by the viscosity of the oil to a point where the damper will fail to damp or moderate the frictional motions as smoothly as required.
One device developed for the purpose of preventing the oil applied inside the damper from being thermally expanded, for example, and consequently forced out of the housing of the damper consists in partitioning the interior of the housing with a flexible membrane, filling one side of the membrane and leaving the other side of the membrane empty. This device permits perfect prevention of the leakage of the oil because the flexible membrane is capable of absorbing any expansion of the oil caused by heat or some other agency. It nevertheless suffers from inevitable complication of construction.